1. Field of the Invention
The present invention relates to a silent structure for a drawing die and a silent run-up unit therefor used when a plate metal part of an automobile or home electric equipment part is processed by the drawing.
2. Description of the Invention
One example of the drawing die is shown in FIG. 6. This drawing die includes a centrally located punch 101, a blank holder 103 fitted over the punch 101 which is vertically movable supported by a cushion pin 102, and a die 104 disposed to oppose to the punch 101 for vertical movement.
A lower die 109 comprising the punch 101 and the blank holder 103 is secured to a bolster 106 of a press machine. An upper die 110 comprising the die 104 is secured to a ram 107 of the press machine, and moves up and down when the press machine is driven. Further, the blank holder 103 is supported by the cushion pin 102. A cushion apparatus of the press machine moves the cushion pin 102 up and down, and the blank holder 103 moves up and down accordingly.
The drawing will be explained. First, the blank holder 103 is lifted by the cushion pin 102 up to a position shown by a phantom line.
Next, the thin plate 108 is placed on the blank holder 103 and the punch 101 as shown by a phantom line.
Thereafter, when the upper die 110 is lowered, the die 104 collides against the thin plate 108 on the blank holder 103 over the entire outer periphery of the punch 101, and the blank holder 103 and the die 104 sandwich the thin plate 108. Subsequently, when the upper die 110 is lowered, the thin plate 108 sandwiched between the blank holder 103 and the die 104 is drawn, and when the upper die 110 reaches the illustrated bottom dead center, the thin plate 108 is drawn into a work area W.
When the upper die 110 is lifted, the blank holder 103 is lifted up to the position shown by the phantom line by a rising force of the cushion pin 102, and the plate in the work area W is released from the punch 101. The die 104 in the upper die 110 is provided with an air vent 105 for preventing a negative pressure from being created between, the plate in the work area W and the die 104 when the plate in the work area W falls by its own weight. Or the plate in the work area W is moved downward and released out from the die 104 by a pushing pin (not shown) biased by a spring, and the plate in the work area W released out by a press machine is sent to that for a next process.
In the above described drawing, when the die 104 collides against the thin plate 108 placed on the blank holder 103, the die 104 collides against the thin plate 108 over the entire outer periphery of the punch 101 simultaneously, and a pressure applied to the cushion pin 102 may reach about 60 to 100 tons, which causes a large noise. In these days when a quiet environment is required, the noise of the drawing die is a serious social problem.
In order to prevent the noise generated when the die collides against the thin plate on the blank holder of the drawing die, an attempt has been made to reduce the noise by providing an urethane rubber or gas spring on the blank holder so that die collides against the urethane rubber or gas spring before the die collides against the thin plate on the blank holder to absorb the shock, but sufficient noise reduction could not be obtained.
Further, an attempt has been made to lower the cushion pressure for only a constant time period at an initial stage of the lowering movement of the cushion pin when the die collides against the thin plate on the blank holder, but it is necessary to improve the cushion apparatus of the press machine, which substantially inflates costs.
In the drawing die, a substantial amount of noise is generated when the die collides against the thin plate on the blank holder, and it is required to reduce the noise as much as possible.